1. Field of the Invention
The present invention relates to an art that variation of cetane number is calculated (estimated) from the angular velocity amplitude of engine rotation so as to correct fuel injection when the cetane number is varied.
2. Background Art
Light oil which is a fuel of a diesel engine is produced and sold at world nations while cetane number of the light oil is varied within the range of 38 to 52. Since light oil used for a diesel engine is measured strictly and then sold, the cetane number of the light oil should always be uniform. However, for example, fuel of a different cetane number may be supplied to a ship at a port of call. Especially, the cetane number of coarse light oil may decrease.
Fuel injection control of a diesel engine is based on the nominal value of the cetane number of the fuel used at the time of production. Then, when the cetane number is not uniform or decreases, appropriate fuel injection control cannot be performed.
In consideration of the background, conventionally, several methods for detecting variation of cetane number have been performed. For example, Patent Literature 1 discloses an art for detecting cetane number at the time of fuel-cutting of an internal-combustion engine.
However, the cetane number of fuel used for driving may be changed by using the status of the fuel or the number of fuel supply, whereby it is preferable to detect variation of cetane number regularly. Conventionally, there is no method for detecting variation of cetane number which can be performed regularly while driving an internal-combustion engine.
Patent Literature 1: the Japanese Patent Laid Open Gazette 2005-344557